1. Field of the Invention
This invention relates to a plastic window panel and, in particular, to a plastic window panel for use in an automotive sun roof.
2. Description of the Related Art
In an automotive sun roof structure, to be in conformity with a reduction in vehicle weight, a sun roof panel consisting of a plastic window panel is used. FIGS. 12 and 13 show an inner slide type sun roof structure in which a plastic sun roof panel 1 moves in the direction of the arrow to be tucked away under a roof 5. Both of the drawings show a state in which the plastic sun roof panel 1 is tucked away, with a roof window 6 provided in the roof 5 being open.
The plastic sun roof panel 1 is a substantially rectangular plate-like member having a uniform thickness and formed of a transparent resin material.
Generally speaking, as compared with a glass panel, the sun roof panel 1 has a lower flexural rigidity and a lower torsional rigidity, so that it is subject to deformation.
When the vehicle runs at high speed, with the roof window 6 being closed, a peripheral edge portion 1a of the plastic sun roof panel 1 undergoes deformation due to the upward attracting force generated by the airflow over the vehicle body. In view of this, a reinforcing member 2 is joined to the plastic sun roof panel 1 by an adhesive 4 so as to extend along the peripheral edge portion 1a of the panel, thereby enhancing the flexural rigidity and torsional rigidity of the plastic sun roof panel 1. Further, the peripheral edge portion of the reinforcing member 2 is bent into an L-shape to form a flange 2a. A weather strip 3, into which the flange 2a is fitted, serves as a seal between the roof window 6 and the plastic sun roof panel 1 when the roof window 6 is closed, preventing intrusion of water into the interior and leakage of air therefrom.
It is to be noted, however, that when heated by sunlight, the plastic sun roof panel 1 exhibits a tendency to expand in the planar direction, which is parallel to the panel surface. However, since the peripheral edge portion 1a of the plastic sun roof panel 1 is glued and secured to the reinforcing member 2, the expansion in the planar direction is significantly restrained. As a result, as indicated by the dotted line in FIG. 13, the plastic sun roof panel 1 undergoes a thermal deformation such that it is arcuately swelled in the vertical direction which is perpendicular to the panel surface.
For the plastic sun roof panel 1 to be tucked away under the roof 5 when opening the roof window 6, it is necessary to secure a gap c between the plastic sun roof panel 1 and the roof 5, taking into consideration the amount d by which the plastic sun roof panel 1 is vertically deformed by heat. Thus, the larger the thermal deformation amount d, the lower the ceiling 8 of the interior, which means it is difficult to ensure a sufficient head clearance hc between the head 7 of the passenger and the ceiling 8.
This invention has been made with view toward solving the above problem in the prior art. It is accordingly an object of this invention to provide a plastic window panel which makes it possible to reduce the thermal deformation and to enlarge the head clearance between the passenger head and the ceiling.
In accordance with this invention, there is provided a plastic window panel comprising a mounting portion defined in a peripheral edge portion and used to mount the panel to a vehicle body, a thin-walled portion which is nearer to a center than the mounting portion, and a central portion defined nearer to the center than the thin-walled portion, wherein the thin-walled portion has a smaller thickness than the central portion.
Further, in accordance with this invention, there is provided a plastic window panel comprising a mounting portion defined in a peripheral edge portion and used to mount the panel to a vehicle body, and an effective view portion having a transparent portion defined on the inner side of the mounting portion, wherein the effective view portion includes a peripheral portion whose thickness is smaller than a virtual thickness necessary for maintaining a predetermined face rigidity in a central portion in the case of a uniform thickness, and the central portion whose thickness is larger than the virtual thickness by an amount compensating for a reduction in face rigidity due to the reduction in the thickness of the peripheral portion.